This invention pertains to a demodulator applicable to the demodulation of polyphase voltages of n phases, interfering among themselves, and which create a system of polyphase pseudo-sinusoidal voltages, modulated in amplitude to a pulsation .epsilon., in order to obtain a system of polyphase voltages of pulsation .epsilon..
The interference between two sinusoidal voltages of frequency f.sub.1, f.sub.2 or pulsation .omega..sub.1, .omega..sub.2, (where .omega..sub.1 =.omega..sub.2= 2.pi.f.sub.2 and .omega..sub.2 =2.pi.f.sub.2 and of different amplitudes U.sub.1, U.sub.2, is a well known phenomenon, currently used in radio, in the technique of synchroscopes, of transmitters, etc.
This phenomenon may be summarized by the following equation: EQU U(t)=U.sub.1 sin .omega..sub.1 t+U.sub.2 sin .omega..sub.2 t=2U.sub.o cos(.epsilon.t) sin (.omega.t)+2e sin (.epsilon.t) cos (.omega.t) (1)
in which
.omega..sub.1 =.omega.+.epsilon.
and
U.sub.1 =U.sub.o +e PA1 .omega..sub.2 =.omega.-.epsilon.
U.sub.2 =U.sub.o -e
with .omega.: average pulsation and U.sub.o =average voltage of the component sinusoidal voltages.
Of course, if two systems of polyphase voltages are placed in series, phase to phase, the result is the production of n voltages U.sub.p analogous to the preceding one and within the same envelope, but staggered between themselves by 2.pi./n, n being the number of phases of each system, such that: ##EQU2## in which p may take all the values from 1 to n.
Further, if the differential voltage e=0, that is if U.sub.1 =U.sub.2 =U.sub.o, the resulting voltage u(t)=2U.sub.o cos .epsilon.t sin .omega.t may be described as a pseudo-sinusoidal voltage of pulsation, .omega., and variable amplitude 2U.sub.o cos .epsilon.t. The same is true for the voltages resulting from the two polyphase systems placed in series, phase to phase, and previously described.
In addition, considering n groups of n voltages resulting from the two polyphase systems of the kind previously described, and if in each case there is performed circular permutations of the phases of the second polyphase system in relation to the first, the result is n groups of voltages with the general characteristics of those of the first group, but the respective envelopes of which are staggered between themselves. The n groups of polyphase voltages U.sub.ip, may be expressed as: ##EQU3## in which i represents the index of the group of voltages and varies from 1 to n, and p represents the index of phase in a group of voltages and varies from 1 to n.
For example for triphase systems, the 3 resulting voltages (U.sub.a.sbsb.1, U.sub.a.sbsb.2, U.sub.a.sbsb.3), (U.sub.b.sbsb.1, U.sub.b.sbsb.2, U.sub.b.sbsb.3), and U.sub.c.sbsb.1, U.sub.c.sbsb.2, U.sub.c.sbsb.3) form three "pseudo-sinusoidal" systems, with variable amplitudes respectively equal to U.sub.A.sbsb.o =2U.sub.o cos .epsilon.t, ##EQU4##
This invention has as an object to provide new appropriate means for using this "pulsating" phenomenon, in particular, to produce a system of polyphase voltages with a given, constant or variable, frequency f, and corresponding to the modulation in amplitude of the component voltages of the said systems of polyphase voltages of the kind described in equation above.
U.S. patent application Ser. No. 33,957 filed on Apr. 27, 1979 in the name of the same applicant entitled "Demodulator of polyphase voltages interfering among themselves", concerns a demodulator of the kind mentioned previously and which comprises a rotating polyphase machine, including basically: (a) n armatures at n phases connected between themselves by a common yoke made up of a low loss material and fed by n systems of polyphase pseudo-sinusoidal voltages modulated in amplitude to a pulsation .epsilon., (b) a rotor freely rotating, including n circuits connected by a common magnetic axle, made up, in its useful parts, of a low loss magnetic material, and (c) n static coils, concentric with the axis of the magnetic axle and at the terminals of which n systems of polyphase voltages of pulsation .epsilon. are collected, which rotating machine is such that each of the n magnetic circuits of the rotor bears a number of polar masses equal to the number of pairs of poles on the corresponding armature, and that the relative geometric keyings of the homologous phases of the n armatures of the stator are identical to the relative longitudinal keyings of the polar masses of the rotor.
Such a demodulator permits the realization of machines, the size and weight of which are relatively small compared to the speeds of rotation which may be very high. However, in such a demodulator, it is important to create altogether a common frame made up of low loss material and a rotor with a common magnetic axle to allow the closing of the lines of the magnetic field. These requirements, in some cases, may turn out to be a hindrance to the extent that they prevent the use of elements from entirely classical electric machines.
This invention aims precisely at permitting the creation of a demodulator of simple design and at a relatively small cost starting from elements of rotating machines especially easy to manufacture from known techniques, in particular, those applied to synchronous machines. These and other goals are met in accordance with the invention by a demodulator applicable to the demodulation of polyphase pseudo-sinusoidal voltages modulated in amplitude to a pulsation .epsilon., in order to obtain a system of polyphase voltages of pulsation .epsilon. by employing a complex of n polyphase synchronous heteropolar rotating machines including n stators at n phases fed by n systems of polyphase pseudo-sinusoidal voltages, modulated in amplitude to a pulsation .epsilon., and of the form ##EQU5## in which i represents the group index of the voltages and varies from 1 to n and p represents the phase index of the group of voltages and varies from 1 to n. Mounted for rotation within the n stators are n wound rotors each including magnetic circuits made up of a low loss magnetic material and capable of passing a magnetic alternating flux without damping, each rotor having the same number of poles as the corresponding stator.
Means to collect from the n rotors, n systems of polyphase voltages of pulsation .epsilon. are also provided.
The means for collecting the n systems of polyphase voltages of pulsation .epsilon. from the n rotors may be readily provided by means of a slip-ring integral with the rotors and fixed brushes contacting the slip-rings.
Thus, in a demodulator according to the invention, there is no need to have a frame and a common axle made up of a low loss material and capable of permitting the passage of a magnetic flux since the machine according to the invention is of a heteropolar kind. In addition, with the exception of using a foliated rotor capable of permitting the passage of an alternating flux, the demodulator according to the invention permits the use of techniques used with synchronous machines.
According to a specific embodiment of the invention, the n stators associated with their rotors constitute n similar synchronous heteropolar machines, mechanically independent. Thus, for example, for a demodulator of the triphase kind, it is enough to associate three synchronous heteropolar machines meeting the conditions which have been mentioned previously, and fed by means of three systems of triphase pseudo-sinusoidal voltages, modulated in amplitude to a pulsation .epsilon., and conforming to the equations (3), to collect on each of the rotor windings a system of pseudo-triphase voltages conforming to the equations (4).
According to another embodiment of the invention, the n stators associated to the n corresponding coiled rotors are mounted on the same frame and the n magnetic circuits of the rotors are supported by a common axle. This embodiment results in a compact machine in which the number of bearings is reduced, and in which the number of slip-rings may also be reduced eventually to the number of magnetic circuits of the rotor plus one, each rotor winding being associated with an independent slip-ring and also to a slip-ring common to the n rotor windings and serving as a neutral.
Other objects, characteristics and advantages of the invention will be better understood upon reading the following detailed description of specific forms of the invention, given only as non-limitating examples, with reference to the attached drawings.